FIG. 1A illustrates a prior art switching regulator with a voltage feedback system 100. As is illustrated, a regulator output voltage of a voltage feedback 105 is compared with a target reference voltage 110 by a comparator 120 for voltage regulation. As is illustrated, a voltage feedback path is used through the comparator 120 to drive an on-off digital control 125, which powers a current driver 127, which is itself coupled to an inductor 130.
The system 100 further includes a power supply 129 coupled to the current driver 127. A power supply de-coupling capacitor 129 is also coupled to the current driver 127, the power supply 129, and ground.
In FIG. 1B, a peak current of the inductor 130 is defined as the maximum value during an inductor current charging state. The valley current of the inductor is defined as a minimum allowable value during an inductor current discharging state during a charge/discharge cycle. Please note that, in the prior art, the peak thresholds are set high to support high load current.
As appreciated by the present inventors, in FIG. 1B, the inductor 130 current magnitude settings are fixed by an external control logic, which is not in the control loop.
Moreover, as appreciated by the present inventors, generally, when a load current is constant, the charge/discharge frequency is also constant. However, when the inductor 130 peak current is high, but the load current transitions to low, the switching frequency of the regulator system 100 becomes lower. As appreciated by the present inventors, the fundamental mechanical frequency of vibration of the de-coupling capacitor 128 is a function of the switching frequency of the regulator 100.
If this mechanical vibration occurs in an audible frequency, this creates noise which is unsuitable and undesirable.
For example, if the charge/discharge cycle occurs on a 2 kHz cycle, which can be heard by human ears, which can be a problem.
FIG. 2 illustrates a transient simulation result of the prior art. The load current is gradually swept up in 210 and swept down in 220 of graph 205. The current peak/valley thresholds are always the same.
The load current is illustrated as low in 240. However, the inductor peak current is the same as occurs in the high load current, so that switching frequency of the regulator 100 is low in 240, so therefore the power supply regulator 100 can lead to unwanted noise emanating from the de-coupling capacitor 128.
FIG. 3 illustrates prior art frequency response simulation result. As is illustrated, a spectrum of the power supply current is observed as occurring in an audible frequency range, when the regulator 100 providing a low load current (e.g., as occurs when a device coupled to the regulator output is turned off).
FIG. 4A illustrates a prior art printed circuit board with a power supply de-coupling capacitor 410 to decouple a power supply (not illustrated) to the regulator components 420. Disadvantageously, the capacitor 410 vibrates at the switching frequency of the regulator 100, and hence, if the regulator switching frequency is in an audible frequency, it results in an audible noise.
Therefore, there is a need in the art as understood by the present inventors to have a form of switching regulator control that addresses at least some of the disadvantages of the prior art.